Leetcode 275. H-Index II

Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm?

接上一篇，数组升序排列。

一看就是二分，需要注意边界，仔细想想。

class Solution {public:    int hIndex(vector<int>& citations) {        int mid = -1, l = 0, r = citations.size()-1;        while(l <= r)        {            mid = (l + r) >> 1;            if(citations.size() - mid == citations[mid]) return citations[mid];            else if(citations.size() - mid > citations[mid]) l = mid + 1;            else r = mid - 1;        }        return citations.size() - r - 1;    }};